A purification step using phenyl Sepharose was developed for isolation of the membrane associated protein components of clostridial glycine reductase. The enzyme complex reconstituted from these two proteins plus the low molecular weight selenoprotein A component catalyzes the reduction of glycine to acetate with concomitant synthesis of ATP. The ability of thiophosphate plus ADP to replace orthophosphate plus ADP indicates that the enzyme system also can form the Gamma-thiophosphate analog of ATP. A synthetic boron analog of glycine, in which the methylene carbon atom is replaced by a boron atom, is an effective inhibitor of the glycine reductase and should be useful in reaction mechanism studies. Another selenoenzyme present in the fatty acid producing anaerobic bacterium, Clostridium kluyveri, was identified as Beta-hydroxybutyryl-CoA dehydrogenase by Maris Hartmanis. This enzyme, like the thiolase from the same organism, contains selenium in the form of selenomethionine. Continued collaborative work on selenium-containing amino acid transfer nucleic acids (tRNAs) from bacterial sources by members of the section resulted in identification of a new selenonucleoside, 5-methylaminomethyl-2-selenouridine. This selenonucleoside is the only selenium-containing nucleoside detected in the tRNAs of Clostridium sticklandii and Escherichia Coli. The methane producing organism, Methanococcus vannielii, contains about equal amounts of 5-methylaminomethyl-2-selenouridine and another unidentified 2-selenouridine as seleno components of the total tRNA population.